Complex sounds such as speech, music, and animal vocalizations contain pronounced spectral and temporal modulations that are perceptually important. The neural coding of spectro-temporal envelopes has been studied extensively in primary auditory cortex (Al), but little is known of their representation in the medial geniculate body (MGB) inputs of Al neurons. We propose to investigate the coding of spectro-temporal envelopes in the MGB of anesthetized ferrets by measuring spectro-temporal response fields (STRFs) with broadband noise stimuli having spectral and temporal modulations. One aim is to test the hypothesis that the Fourier transform phase of the STRF predicts response properties traditionally derived with tones and click trains. Another aim is to quantify how well the STRF predicts the response of MGB neurons to arbitrary spectro-temporal envelopes. A final aim is to make functional models of the transformation between STRFs measured in the MGB to STRFs previously measured in Al. We will test the hypothesis that the sensitivity of Al neurons to the direction of movement of spectral envelopes comes from the convergence of MGB neurons that are all insensitive to the direction of spectral envelope movement and that all process temporal modulations in almost the same way. When combined with previous data from Al, this research addresses fundamental issues in thalamo-cortical signal processing such as which properties of Al neurons are synthesized intrinsically and which are inherited from the MGB. By providing information on the representation of an important aspect of speech, this research may help improve processors for auditory implants by giving information tailored for the MGB and cortex.